Certain details of the construction of pipe flanges are made uniform in the interest of standardization and interchangeability. For example, the American Standards Association and the American Petroleum Institute specify a pipe flange having a raised face, that is a flange face a central reduced diameter portion of which is relatively projected. The raised face, annular in shape, provides a sealing surface and a sealing member, for example an O-ring, is placed between opposed sealing surfaces of mating flanges. Outwardly of the raised sealing surface the flange has a circle of bolt holes. Mating flanges, bolted together, compress an installed O-ring and seal the defined joint. Because installations of this kind lack a groove to receive the O-ring, there are no means to give the O-ring a positive back-up, no means to limit compression of the O-ring and no means properly to locate an installed O-ring and to hold it so located while a joint is being closed. The use of a retainer ring has been suggested and this will serve to provide positive back-up and to limit compression. It does not, however, solve the problem of properly locating or centering the O-ring except that it is possible to make the retainer ring sufficiently broad that its outer periphery will limit against the circle of bolts which surround it. This solution is not an entirely satisfactory one since it does not help in an initial positioning of the O-ring. Also, in each size in the range of sizes to which pipe flanges are made, flanges have a varying breadth and weight according to the pressure of the fluid in flow. This means the circle of bolts will define a different diameter at different fluid pressures and further means that for each expected pressure in a given pipe flange size there must be provided an O-ring retainer of respective predetermined outside diameter. Obvious disadvantages inhere in thus adding to inventory and part selection problems.
Aspects of the problem to which this invention is addressed have been recognized in prior art patents, as for example U.S. Patent to Sheesley et al No. 3,531,133 and U.S. Patent to Black No. 3,721,452. In both instances, however, concept of use of the bolt circle as the positioning means is adhered to. In Sheesley et al it is suggested that the encircling spacer ring could be made separable from the sealing member and replaced with one of different outside diameter corresponding to the diameter of a differently encountered bolt circle. Black makes the same general suggestion but contemplates that the encircling spacer ring be constructed of separable annular parts. Thus a portion of the Black spacer ring can be detached and discarded when it becomes necessary to accommodate to a smaller bolt circle.